1. Field of the Invention
This invention relates in general to laser diode communication signals by way of light waveguides and in particular to a system for prolonging the life of a laser diode.
In the invention a circuit arrangement is provided with a laser diode for transmitting communication signals through a transmission link which includes a light waveguide and wherein a transmitting device with a modulator which contains the laser diode and a receiving device receives the output of the laser diode through the light waveguide and supplies through a return circuit a control signal to the transmitter to control the optical output power of the laser diode through a regulating device.
2. Description of the Prior Art
A circuit arrangement for transmitting communication signals through a light waveguide is known, for example, in the publication "Nachrichtenubertragung mit Lichtwellenleiter", telecom report, 1 (1978), Vol. 1, pages 34 to 39.
In the known circuit arrangement, a communication signal is supplied as a modulating signal to an electro-optical transducer which consists of a laser diode. The light produced by the electro-optical transducer or from the light source is transmitted through a light waveguide to a light receiver at a receiving location.
The use of a laser diode as the transmitting end light source has the advantage that it can be modulated easily into the gigahertz range and it possesses sufficient light power which can be coupled into the light waveguide and which is for example, 15 to 20 dB higher than luminescence diode. However, a disadvantage results in that shorter life duration of the laser diode results with this system.
Difficulties can arise when the laser diode has a steep gradient characteristic curve which is influenced by temperature and aging. Additional difficulties result from the fact that similar temperature and aging factors occur in the excited laser modes which can be difficult to completely control.
The life duration of a laser diode is dependent upon the quantity of admitted light and, thus, it is desirable to regulate the operating point of the laser diode such that it emits precisely the required amount of light to the light waveguide.
German OS 27 12 293 discloses how to construct laser control circuits such that the optical output energy of a laser is controlled by a relatively slow feedback loop which determines the mean value of the optical output energy of the laser. A voltage derived from the optical output energy is compared with a fixed reference voltage so as to control the forwards current through a differential amplifier.